Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
FIG. 1 illustrates an LED with a laminated phosphor layer, described in more detail in WO 2012/023119 A1. The abstract states “A method is described for laminating a layer (28) over an array of LED dies (10) on a submount wafer (12). The layer (28) may comprise phosphor powder in a silicone binder. The layer is formed on a support film then dried. The layer is then mounted over the LED dies (10), and the structure is heated in a vacuum. Downward pressure is placed on the support film so that the layer adheres to the tops of the LED dies and forms an airtight seal around the periphery of the wafer. The structure is then exposed to ambient air, and the support film is removed. The seal prevents ambient air from entering between the layer (28) and the wafer (12). In a second lamination step, the structure is heated to a higher temperature in a vacuum to remove the remaining air between the layer and the wafer. The structure is then exposed to ambient air pressure, which conforms the heated layer to the LED dies.”